Crimping is a well-known method of attaching a terminal to a conductor. For a strong and electrically efficient crimped connection, the terminal must be deformed sufficiently to provide solid metal-to-metal contact with the conductor, but the terminal and conductor must not be overstressed to the point where the metal is weakened and fractured. A common non-destructive method of determining the quality of a crimped connection is by measuring the crimp height, i.e., the vertical dimension of the terminal after crimping. The measured crimp height is compared with a target crimp height which has previously been determined, by one or more of various possible mechanical and electrical tests, to be desirable for the particular style, size, and material of the terminal and conductor which are being used. Terminals having a crimp height which is outside of the tolerance range for the target crimp height are rejected as defective.
The crimp height of many terminals cannot be readily measured. This may be due to an unusual crimp configuration having a surface profile which cannot be accurately engaged by a measuring probe, and/or the presence of insulation on the terminal which may pull away from the surface of the terminal and generate a false reading. Historically, this problem was addressed by the use of bottoming dies having opposed stop, or bottoming, surfaces which are arranged to engage, or bottom, against each other when the dies are fully closed. The bottoming dies are configured so that when the dies are driven together and the stop surfaces have bottomed, a terminal engaged between the dies will have been deformed to the correct crimp height. Bottoming of the stop surfaces provides an indication that the terminal has been fully crimped and prevents excessive deformation of the terminal. Therefore, the inability to accurately measure the crimp height becomes immaterial.
A problem with the use of bottoming dies is that defects in crimping tools or processes may prevent the dies from bottoming. Such defects include deflection of drive components or tool frames, loose or worn parts, improper set-up, and dirt, among others. It is impossible to determine visually whether die closure has occurred in every case. In some cases the stop surfaces may come quite close together without actually bottoming, and even these cases may result in defective crimps when the crimp height tolerance is only a few thousandths of an inch. There is a need for a crimping apparatus of the type having bottoming dies which has a means for verifying whether the dies have fully closed in every case.